DE102011002434A1 - Method for evaluating filtering effect of particulate filter in exhaust gas passage of diesel engine in motor car, involves evaluating filtering effect of particulate filter from soot mass, soot concentration or filtering efficiency - Google Patents

Abstract

The method involves calculating a mean value (18) from tripping time for an exhaust gas volumetric flow, exhaust gas temperature and a difference between the exhaust gas temperature and temperature of a particle sensor during a measurement cycle of the particle sensor. A soot mass and soot concentration or filtering efficiency of the particulate filter are determined (23) from the tripping time and the mean value, and filtering effect of the particulate filter is evaluated (24) from the soot mass, the soot concentration or the filtering efficiency. An independent claim is also included for a device for evaluating filtering effect of a particulate filter in an exhaust gas passage of a combustion engine.

Description

State of the art

The invention relates to a method for evaluating the filter effect of a particulate filter in the exhaust passage of an internal combustion engine, wherein an exhaust gas temperature, an exhaust gas volumetric flow, an output signal of a particle sensor disposed in the exhaust duct downstream of the particulate filter and the temperature of the particulate sensor are detected in a control unit and wherein for evaluating the particulate sensor a trigger duration is determined from the beginning of a measurement cycle until reaching a triggering threshold of the output signal.

The invention further relates to a device for evaluating the filter effect of a particulate filter in the exhaust passage of an internal combustion engine, wherein in the exhaust passage downstream of the particulate filter, a particle sensor is arranged, wherein the internal combustion engine, a control unit for controlling the internal combustion engine, for controlling the particle sensor and for determining a trip duration is associated with the particle sensor and wherein sensor elements or computing rules are provided in the controller for determining an exhaust gas temperature, a temperature of the particulate sensor and an exhaust gas volumetric flow.

Statutory regulations stipulate today for the operation of internal combustion engines the observance of strict emission limit values for the resulting exhaust gas components. In order to meet these limits, catalysts and filters are provided in the exhaust ducts of the internal combustion engines, the function of which is to be monitored during the driving operation, for example in the context of an on-board diagnosis (OBD). In addition to the catalysts and filters, a multiplicity of sensors, for example in the form of exhaust gas sensors for determining constituents of the exhaust gas or in the form of temperature sensors for measuring the exhaust gas temperature, are arranged in the exhaust gas duct for this purpose. The sensors are used to control the internal combustion engine and monitor the function of the exhaust aftertreatment system in the context of on-board diagnostics (OBD).

For diesel engines particulate filters are provided in the exhaust passage, which filter the resulting soot particles from the exhaust gas during combustion. If the storage capacity of such a particulate filter is reached, the accumulated soot particles are burned during a filter regeneration phase. Particle sensors arranged after and in front of the particle filter make it possible to monitor the function of the particle filter and to determine the time of a necessary regeneration of the particle filter.

Particle sensors are exemplary in the DE 10149333 A1 and the WO 2003006976 A2 described. These are resistive particle sensors that evaluate a change in the electrical properties of an interdigital electrode structure due to particle accumulation. There may be provided two or more electrodes which mesh with each other like a comb. By an increasing number of particles attached to the particle sensor, the electrodes are bridged, resulting in a decreasing with increasing particle deposition electrical resistance, a decreasing impedance or a change in a resistor or impedance related characteristic such as a voltage and / or current effect. For evaluation, a threshold value, for example a measuring current between the electrodes, is generally determined and the time until the threshold value is reached is used as a measure of the accumulated particle quantity. Alternatively, a signal change rate during the particle accumulation can be evaluated. If the particle sensor is fully loaded, the deposited particles are burned in a regeneration phase with the aid of a heating element integrated in the particle sensor. To regulate the regeneration, the temperature of the particle sensor is determined by means of an integrated temperature sensor, for example a printed metallic meander. After regeneration, a new measurement cycle can be started.

In Scripture DE 10 2005 034 247 a method for monitoring an exhaust gas limit value of an internal combustion engine is described by means of an engine control, wherein the engine controller has at least one exhaust gas sensor and wherein an error signal is emitted when exceeding the exhaust gas limit value. The predicted for the current driving condition emissions are determined using an engine model and compared with the signal of the exhaust gas sensor or a derived comparison value for the emission. The exhaust gas sensor may be a collecting particle sensor arranged behind a particle filter. In order to judge whether the particulate filter is intact or defective, the comparison of an emissivity calculated as a quotient of the particulate emission measured by the particulate sensor and the modeled particulate emission with a predetermined limit value is proposed. The limit value is specified for a boundary-type particle filter which still just complies with the prescribed emission limit values during predetermined, standardized driving cycles. The method makes it possible to monitor the exhaust gas when the operating conditions of the internal combustion engine deviate from the limits in comparison with standardized driving cycles.

The disadvantage here is the complex signal analysis and the equally complex comparison with a signal behavior model with the corresponding computational and memory overhead in the engine control.

It is an object of the invention to provide a method and a device which allows easy monitoring of the proper functioning of particulate filters in the exhaust passage of internal combustion engines.

Disclosure of the invention

The object of the invention relating to the method is achieved in that during the measuring cycle of the particle sensor over the triggering time at least for the exhaust gas volumetric flow, the exhaust gas temperature and a difference between the exhaust gas temperature and the temperature of the particulate sensor, in each case an average value is formed and stored and that from the mean values and the triggering duration of a soot mass entrained after the particulate filter in the exhaust gas, a soot concentration or a filter efficiency are determined, and the filtering effect of the particulate filter is evaluated from the soot mass, the soot concentration or the filter efficiency. The method enables a simple correlation of the output signal of the particle sensor with the filtering effect of the particle filter, without having to carry out a complex signal analysis and a comparison with a signal behavior model. The soot mass detected after the particulate filter during the triggering period, the soot concentration and the filter efficiency are dependent on the filtering effect of the particulate filter. The filter efficiency initially shows a relatively high inaccuracy, since no adjustment is made with a soot emissions. It is advantageous that the exhaust gas volume flow, the exhaust gas temperature and the temperature of the particle sensor in exhaust ducts of modern internal combustion engines are monitored anyway. The values are therefore available to a higher-level control unit and no additional components need to be provided for carrying out the method. The formation of the mean values during a measurement cycle of the particle sensor is possible with little computational effort. Exhaust gas volumetric flow, exhaust gas temperature and the difference between the exhaust gas temperature and the temperature of the particulate sensor and the associated output signal of the particulate sensor correlate with the particulate emission after the particulate filter. From the average values, it is therefore possible, under suitable conditions, to simply determine a sufficiently accurate particle emission value by particle filter during the measurement cycle in the form of the soot mass or the soot concentration or directly in the filter efficiency.

A simple determination of the soot mass, the soot concentration or the filter efficiency can be achieved by determining the soot mass, the soot concentration or the filter efficiency from a first characteristic map stored in the control unit from the mean values and the release duration. In this case, the first map can be stored as a multi-dimensional map in the control unit. The particle sensor represents with its signal over the specific trip duration a kind of vector, which refers in the multi-dimensional map to the level for determining the emissions in the measurement period from the average values of the exhaust gas volumetric flow, the exhaust gas temperature and the difference between the exhaust gas temperature and the temperature of the particulate sensor.

When using the internal combustion engine in a motor vehicle, it may be provided that the filter effect of the particulate filter is evaluated from the soot mass determined from the first characteristic map, based on the distance traveled during the trip duration.

According to a particularly preferred embodiment of the invention, it may be provided that in the control unit a second map for a soot emission of the internal combustion engine as a function of load and speed is stored, that from the occurring during the measurement cycle values for the load and the speed of the internal combustion engine the second characteristic field, the Rußrohemission is determined until reaching the triggering threshold of the particle sensor and that the filtering effect of the particulate filter is evaluated by comparing the determined from the first map soot mass or soot concentration with the Rußrohemission. The comparison of the determined from the first map soot emission (soot mass or soot concentration) after the particulate filter with the present before the particulate filter soot emission allows a more accurate determination of the filtering effect of the particulate filter. The second map can be recorded typical of a vehicle during an engine application, for example, based on a specific and typical combination of load and speed of the internal combustion engine in free driving.

If it is provided that the filter effect of the particulate filter is determined during specified operating cycles of the internal combustion engine, the accuracy of the method can be significantly improved. This applies in particular to the filter efficiency determined directly from the first characteristic map. The particulate emission is highly dependent on the load and the speed of the internal combustion engine during the measurement cycle. For heavy changes in load and speed during the measuring cycle, the mean values of the exhaust gas flow, the Exhaust gas temperature and the difference of the exhaust gas temperature and the temperature of the particle sensor and the average particle emission determined therefrom, the actual particle emission insufficient, which can lead to corresponding errors in the evaluation of the filter effect of the particulate filter. For specified operating cycles with predetermined load and speed changes during the particle sensor measurement cycle, the accuracy of the evaluation can be significantly improved. For motor vehicles powered by the internal combustion engine, corresponding driving cycles may be specified for this purpose.

The accuracy in the determination of the filter effect can be further increased by the fact that the filtering effect of the particulate filter is determined from measuring cycles, which have a small standard deviation of the values of the exhaust gas volumetric flow, the exhaust gas temperature and the difference between the exhaust gas temperature and the temperature of the particulate sensor or the measuring cycles with lower standard deviation of the values of the exhaust gas flow rate, the exhaust gas temperature and the difference between the exhaust gas temperature and the temperature of the particulate sensor are weighted more heavily in the evaluation of the filtering action and weighting scales with large standard deviation at one of the sizes. The determined soot emission values and soot emission values have an increased accuracy if the exhaust gas parameters exhaust gas volumetric flow, exhaust gas temperature and the difference between the exhaust gas temperature and the temperature of the particulate sensor ascertained during the measuring cycle have only slight variances.

In order to increase the safety in the evaluation of the function of the particulate filter and to avoid misinterpretations regarding the filter effect due to individual erroneous measurements, it may be provided that several measurement cycles of the particulate sensor are taken into account for the evaluation of the filter effect of the particulate filter.

The object of the invention relating to the device is achieved in that the control unit has a program routine for forming in each case an average value of the exhaust gas temperature, the exhaust gas volume flow and the difference between the exhaust gas temperature and the temperature of the particle sensor during the triggering time and in the control unit a first characteristic map for Determining a Rußmasse, a soot concentration or a filter efficiency from the averages and the duration of the release of the particulate sensor is deposited. The output signal of the particle sensor forms a reference into the region of the multidimensional first characteristic map in which the soot emission is derived from the average values. Since the control unit of modern internal combustion engines sensor signals are supplied to the exhaust gas temperature and the temperature of the particle sensor and also the necessary information for determining the exhaust gas flow, the determination of the filter effect can be implemented without additional components by a software extension of the control unit. An elaborate signal analysis and comparison with a signal behavior model can thus be dispensed with.

The determination of the filter effect on the basis of the average values of the exhaust gas temperature, the exhaust gas volume flow and the difference between the exhaust gas temperature and the temperature of the particle sensor during the triggering period may initially be heavily faulty. Therefore, provision may be made for a second characteristic map for determining a soot emission of the internal combustion engine from a load and a rotational speed to be provided in the control unit, and for a program routine for comparing the soot mass or the soot concentration with the soot emission during the triggering period to evaluate the filter effect , By comparing the soot emission determined after the particulate filter with a particulate matter emission present in front of the particulate filter, the accuracy of the method can be significantly improved.

Short description of the drawing

The invention will be explained in more detail below with reference to an embodiment shown in the figure. It shows:

1 a flow chart for evaluating the filtering effect of a particulate filter.

1 shows a flowchart for evaluating the filtering effect of a particulate filter in the exhaust passage of an internal combustion engine. For this purpose, a resistive particle sensor with integrated temperature sensor in the exhaust gas direction behind the particle filter to be monitored is arranged.

In a first function block upstream of the actual measurement 10 the regeneration of the particle sensor takes place, in which deposited soot particles are burned with the aid of a heating element integrated in the particle sensor and the particle sensor is set in a defined initial state. In a second function block 11 the start of a measuring cycle takes place. During the measurement cycle is in a fourth function block 13 an exhaust gas flow rate determined and therefrom in a sixth function block 15 an average value for the exhaust gas volume flow over time since the start of the measurement cycle is formed. At the same time, in a third function block 12 measured the exhaust gas temperature and from it in a fifth function block 14 an average of the exhaust gas temperature is calculated. Via the temperature sensor integrated in the particle sensor will be in a seventh function block 16 the temperature of the particle sensor determined. In an eighth function block 17 a difference between the exhaust gas temperature and the temperature of the particulate sensor is determined and this in a ninth function block 18 averaged over the measuring cycle.

During the measuring cycle takes place in a tenth function block 19 a measurement of the current flow through the sensor element of the particle sensor. The electrical conductivity of the sensor element is brought about by the particles deposited from the exhaust gas stream on the sensor element and enables the flow of current, which is therefore a measure of the loading of the particle sensor and thus of the particle content in the exhaust gas. After the regeneration of the particle sensor in the function block 10 In a phase of the measurement cycle without current flow, first of all a sufficient amount of particles is deposited in order to form bridges of soot particles between the electrodes of the particle sensor. After this phase without current flow, the current through the particle sensor increases and it is in a query 20 decided whether the measuring cycle is ended. The termination of the measurement cycle occurs when the current through the particle sensor reaches a predetermined triggering threshold or when the change in current reaches a predetermined value. The value for the current change can be specified as an example 10 μA. If the measurement cycle is not completed, the flowchart will show the second function block 11 branches and the measuring cycle continues.

Will in the query 20 decided that the measurement cycle is terminated, is in a twelfth function block 22 determines a triggering time for the particle sensor, which corresponds to the duration from the start of the measurement cycle until reaching the triggering threshold of the particle sensor or the duration for a given current change of 10 μA example corresponds. Subsequently, in a thirteenth function block 23 From a multi-dimensional first map, a soot emission from the trip duration and in the fifth, sixth and ninth function block 14 . 15 . 18 certain mean values. The soot emission and one in an eleventh function block 21 In a fourteenth function block, soot emissions determined from a second characteristic map of load and rpm values are determined 24 compared. From the comparison in the fourteenth function block 24 the filter effect of the particulate filter is evaluated and concluded on a compliance or exceeding of the specified limits.

To carry out the method, the particle sensor is first regenerated after a request from the control unit to evaluate the filter effect of the particle filter. During the subsequent measuring cycle, the occurring exhaust gas volume flows, exhaust gas temperatures and differences between exhaust gas temperatures and temperatures of the particle sensor are recorded and averages are formed for the respective parameters and state variables of the exhaust gas. When the current flow through the particle sensor reaches the tripping threshold, the current averages and the tripping duration are stored from the beginning of the measurement cycle until the tripping threshold is reached. From these values, the soot emission present after the particulate filter in the form of a soot mass or a soot concentration or directly a filter efficiency of the particulate filter is determined from the multidimensional first characteristic map. The filter efficiency will have a relatively high inaccuracy, since no adjustment is carried out via a Rußrohemission. However, it can be used directly for evaluating the filter effect with small deviations of the exhaust gas parameters from the respective mean value. In particular, in a previously specified driving cycle high accuracies can be achieved.

From a second map, the occurring Rußrohemission is determined depending on the load and the speed of the internal combustion engine. The data set for the second characteristic map is generated beforehand in a vehicle-specific determination of the soot emissions produced as a function of typical load and rotational speed operating points of the internal combustion engine, for example in free driving mode. The filter effect of the particulate filter is determined by comparing the soot emission determined from the first characteristic map with the particulate matter emission from the second characteristic map before the particulate filter and compared with the requirement for a boundary particle filter. It must be taken into account that the soot emissions per route, determined from a load / speed regime, may be above a certification limit, since the limit values for soot emissions must only be complied with for a standardized load / speed regime within a given drive cycle.

A higher accuracy in the determination of the filter effect can also be achieved if the exhaust gas parameters exhaust gas volume flow, exhaust gas temperature and difference between the exhaust gas temperature and the temperature of the particle sensor determined during the measuring cycle have only slight variances. The variance can be evaluated, for example, by the standard deviation of the means. Results from measurement cycles with high standard deviations can be neglected or evaluated with a lower weighting.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10149333 A1 [0005]
• WO 2003006976 A2 [0005]
• DE 102005034247 [0006]

Claims (9)

Method for evaluating the filter effect of a particulate filter in the exhaust passage of an internal combustion engine, wherein an exhaust gas temperature, an exhaust gas volumetric flow, an output signal of a arranged in the exhaust passage after the particulate filter sensor and the temperature of the particulate sensor are detected in a control unit and wherein for evaluation of the particulate sensor, a release duration of the Beginning of a measurement cycle is determined until reaching a triggering threshold of the output signal, characterized in that during the measurement cycle of the particle sensor over the triggering time at least for the exhaust gas volumetric flow, the exhaust gas temperature and a difference between the exhaust gas temperature and the temperature of the particulate sensor each an average value is formed and stored and that from the average values and the duration of the release, a soot mass entrained after the particulate filter in the exhaust gas, a soot concentration or a filter efficiency are determined, and that the soot mass, the soot concentration or the filter efficiency, the filter effect of the particulate filter is evaluated. Method according to Claim 1, characterized in that the soot mass, the soot concentration or the filter efficiency are determined from a first characteristic map stored in the control unit from the mean values and the duration of the release. A method according to claim 1 or 2, characterized in that the filtering effect of the particulate filter from the determined from the first map soot mass is evaluated based on the covered during the trip duration route. Method according to one of claims 1 to 3, characterized in that in the control unit a second map for a Rußrohemission of the internal combustion engine as a function of load and speed is deposited, that from the occurring during the measuring cycle values for the load and the speed of the internal combustion engine the second characteristic field, the Rußrohemission is determined until reaching the triggering threshold of the particle sensor and that the filtering effect of the particulate filter is evaluated by comparing the determined from the first map soot mass or soot concentration with the Rußrohemission. Method according to one of claims 1 to 4, characterized in that the filtering effect of the particulate filter during specified operating cycles of the internal combustion engine is determined. Method according to one of claims 1 to 5, characterized in that the filtering effect of the particulate filter from measurement cycles is determined, which have a small standard deviation of the values of the exhaust gas volumetric flow, the exhaust gas temperature and the difference between the exhaust gas temperature and the temperature of the particulate sensor or that measuring cycles with less Standard deviations of the values of the exhaust gas volumetric flow, the exhaust gas temperature and the difference between the exhaust gas temperature and the temperature of the particulate sensor are weighted more heavily in the evaluation of the filtering effect and the weighting of measuring cycles with a large standard deviation is lower. Method according to one of claims 1 to 6, characterized in that for the evaluation of the filtering effect of the particulate filter several measuring cycles of the particulate sensor are taken into account. Device for evaluating the filter effect of a particulate filter in the exhaust passage of an internal combustion engine, wherein in the exhaust passage downstream of the particulate filter, a particle sensor is arranged, wherein the internal combustion engine is associated with a control unit for controlling the internal combustion engine, for controlling the particle sensor and for determining a release duration of the particulate sensor and wherein sensor elements or calculation rules are provided in the controller for determining an exhaust gas temperature, a temperature of the particulate sensor and an exhaust gas volumetric flow, characterized in that the control unit a program routine for forming an average of the exhaust gas temperature, the exhaust gas volumetric flow and the difference between the exhaust gas temperature and the temperature of Particle sensor during the triggering duration and that in the control unit, a first map for determining a Rußmasse, a soot concentration or a filter efficiency a us the mean values and the release time of the particle sensor is deposited. Apparatus according to claim 8, characterized in that in the control unit, a second characteristic map for determining a Rußrohemission of the internal combustion engine of a load and a speed is provided and that a program routine for comparing the Rußmasse or the Rußkonzentration with the Rußrohemission during the triggering time to evaluate the filtering effect is provided.

Images